A glycol is an organic compound with two hydroxyl groups attached to different carbon atoms thereof. Particularly, neopentyl glycol (NPG), which is a white crystalline material with a melting point of 129.13° C., is an important intermediate of various synthetic resins. In addition, NPG is widely used industrially as a raw material of various plastic powder coatings, synthetic lubricants, plasticizers, surfactants, textile finishing agents, and the like.
Such NPG is generally prepared by aldol-condensing isobutyraldehyde with formaldehyde to produce hydroxypivaldehyde (HPA), and then reacting HPA with hydrogen in the presence of a catalyst as in Formula 1 below:

In aldol condensation between isobutyraldehyde and formaldehyde, an alkali metal compound, such as an alkaline hydroxide or an alkaline carbonate, has been used as a catalyst. However, when such alkali metal compounds are used, a large amount of organic acid salts is generated and there have been problems in separating and treating by-products thereof.
In U.S. Pat. No. 3,808,280, a tertiary amine was used as a catalyst useful for aldol condensation reaction. Although the yield of HPA increases when aldol condensation is performed using a tertiary amine, a tertiary amine salt, which is generated due to reaction of the tertiary amine with organic acid in a reaction mixture, inactivates a hydrogenation catalyst such as Raney nickel. In addition, the tertiary amine salt decomposes HPA at high temperature, which is a direct cause of NPG yield decrease and catalyst poisoning.
As a main by-product of aldol condensation reaction, isobutyl aldoxane, NPG-isobutyrate, or the like is generated. Such isobutyl aldoxane, NPG-isobutyrate, or the like is converted into a by-product, such as isobutanol or trimethylpentanediol (2,2,4-trimethyl-1,3-pentanediol; TMPD), by hydrogenation. Since these by-products have a boiling point similar to that of NPG, it is very difficult to isolate the same by distillation.
In U.S. Pat. No. 4,885,515, a triethylamine catalyst was not isolated from a product of aldol condensation reaction, and hydrogenation was directly performed using a copper chromite catalyst containing manganese. However, such hydrogenation should be performed under conditions of high temperature and high pressure, thereby requiring expensive equipment. In addition, since a catalyst is inactivated during hydrogenation, the catalyst should be replaced. These are disadvantages preventing commercialization of the method.
In U.S. Pat. No. 4,851,592, hydrogenation was performed in a slurry state using Raney nickel by means of a gas-sparging reactor. However, in this case, since crude HPA is directly fed into a hydrogenation reactor when hydrogenation is performed, catalyst poisoning due to the organic acid salt of a tertiary amine or unreacted substances, which are contained in a reactant, is serious. Accordingly, there are problems in performing the hydrogenation for a long time.
In addition, since an aqueous formaldehyde solution containing 8 to 15% by weight of methanol is used as a reactant in conventional aldol condensation reaction, methanol is discharged along with wastewater after the reaction. Accordingly, a separate process of separating and distilling methanol is required. Therefore, the process is complicated and equipment costs are high.
Crude NPG, which is a hydrogenation product, includes TMPD, hydroxypivalic acid NPG ester (HPNE), and the like. Since TMPD and HPNE have boiling points very similar to that of NPG, it is impossible to isolate the TMPD and HPNE by simple distillation. In addition, since, when a reaction mixture is distilled, HPNE is unstable and the yield of NPG is decreased, sodium hydroxide is added to be converted into NPG by saponification in the industry. However, since HPA or sodium salts of other organic acids, which have been generated by saponification, promote decomposition reaction of NPG at a high temperature of 140° C. or more, a distillation process is restricted. In addition, it is impossible to remove TMPD that is not converted into a nonvolatile sodium salt during saponification.
Accordingly, various methods of purifying NPG from crude NPG have been suggested. For example, a method of extracting using a solvent, a vacuum distillation method, a crystallization method, and the like have been suggested. However, these methods are not economical and commercialization thereof is thus difficult.
U.S. Pat. No. 2,895,996 proposed a method of sublimating crude NPG by saponification to obtain high-purity NPG. Here, a distillation temperature is limited to 70° C. to 140° C. to prevent decomposition of NPG by sodium salt, whereby the temperature of an upper part of a sublimation apparatus is low. Accordingly, the method is uneconomical.
U.S. Pat. No. 4,935,555 proposed a method of distilling NPG by means of a thin-film vacuum distillation apparatus. However, the method is uneconomical due to high equipment costs. In addition, the recovery rate of NPG is decreased due to side reactants and distillation residues and it is impossible to isolate TMPD that is not converted into a salt during saponification, whereby purity is decreased.
Therefore, attempts to produce NPG in high yield and using economical manner are ongoing.